An inline ion-exchange system in a chemiluminescence-based analyzer for direct analysis of N-nitrosamines in treated wastewater.

A newly developed, ion exchange-based inline pretreatment system was used to mitigate the effect of background constituents in natural water and treated wastewater to achieve rapid, reliable, and sensitive analysis of N-nitrosamines. The pretreatment system (anion exchange module, AEM) was incorporated into a high-performance liquid chromatograph (HPLC) coupled with a photochemical reactor (PR) and chemiluminescence (CL) detector (HPLC-PR-CL), which can analyze four hydrophilic N-nitrosamines at ng/L levels. This system requires no pre-concentration of the water sample nor the use of deuterated surrogates, unlike other conventional N-nitrosamine analytical techniques. The AEM converted anions in the eluent to hydroxide ions after HPLC separation and increased eluent pH, allowing for the subsequent photochemical reactions, which are otherwise achieved by pH conditioning with an additional dosing pump of basic chemical. The AEM also removed anionic interfering compounds (e.g. nitrate) from the samples, allowing for improved N-nitrosamine analysis in treated wastewater. The operating conditions of the AEM and PR were optimized to obtain sensitive and stable analytical performance. As a result, the lowest-concentration minimum reporting levels of N-nitrosodimethylamine, N-nitrosomorpholine, N-nitrosomethylethylamine, and N- nitrosopyrrolidine using the optimized system were 0.42, 0.54, 0.58, and 1.4 ng/L, respectively. The improved analytical method was validated by comparing the results with a conventional method based on gas chromatography coupled with a mass spectrometric ion trap detector. These results indicated that HPLC-PR-CL equipped with an inline AEM can be competitively applied as a rapid analytical technique for the determination of N-nitrosamines in various water matrices.

In-line System to Produce High-Purity Acid Solutions.

Herein, we report a new device that generates a high-purity acid solution. It comprises three compartments divided by anion-exchange membranes and filled with ion-exchange resins. Fluorochemical cation-exchange membranes, which tolerate electrochemical wear and permit bulk flow, are inserted between each electrode and the anion-exchange resin. A bipolar boundary is a composite boundary comprising anion and cation exchangers. This device has four bipolar boundaries to separate the location of acid generation from the location where water is electrolyzed. It can tolerate high pressures, resist degradation due to electrolysis at the electrodes, and produce high-purity acid solutions that are free from gases and cationic impurities. The acid solution is generated on the basis of an electrokinetic phenomenon at the surfaces of ion-exchange resins and membranes in an electric field; its concentration can be controlled at rates from 0.01 to 100 µmol/min by adjusting the electrical current applied to the device.

Device to generate high purity hydroxide solution in-line for ion chromatography.

Herein, we report a new device that generates a high-purity hydroxide solution in line. The device's container has three compartments that are isolated from each other by two cation exchange (CE) membranes. In each end of the container, an electrode is installed. The three compartments are filled with ion exchange resins. A bipolar boundary is a composite boundary comprising anion- and cation-exchangers. This device has two bipolar boundaries, which are used to separate the location of hydroxide solution generation from the location where water is electrolyzed. Therefore, it can produce high-purity hydroxide solutions that are free from gases and anionic impurities. The hydroxide solution is generated on the basis of an electrokinetic phenomenon at the surfaces of ion-exchange resins and membranes in an electric field; NaOH concentration can be controlled at rates from 0.01 to 100mM per 1mL/min by adjusting the electrical current (0-200mA) applied to the device. As the generated solution is used as an eluent for a suppressed anion chromatography, the electrical conductivity of the effluent from the suppressor is as low as that of ultra-pure water. Thus, the noise of the base-line electrical conductivity is improved, and so the detection limit of anions on the sub-ng/mL order can be achieved.

Selective removal of carbon dioxide contained in the effluent from ion chromatography suppressors using a new non-vacuum device.

In this paper, a new CO2 gas removal device optimized to selectively remove CO2 gas contained in the effluent from suppressors used in ion chromatography (IC) under non-vacuum conditions is described. This device consists of a closed vessel equipped with gas permeable tubing (GPT) and a CO2 adsorbent. During operation, the CO2 adsorbent adsorbs CO2 gas in the vessel, creating CO2 partial pressure difference between the inside of the GPT and the vessel. The CO2 gas contained in the effluent being pumped into the GPT is selectively removed from the effluent based on the diffusion of the CO2 associated with the CO2 partial pressure difference. The purpose of this study is to optimize the IC operating conditions with the aim of selectively removing HCO3(-) (CO3(2-)) contained in the effluent and reducing the electrical conductivity of the effluent under non-vacuum conditions. The electrical conductivity of the effluent and the signal intensity of the water dip is decreased by approximately 25 µS/cm (from 30 to 5 µS/cm) and by approximately twentieth, respectively, using the optimized CO2 remover. In addition, the anion detection limit achieved in IC instruments with a CO2 remover is on the order of a few ppb.

Development of a new suppressor for the ion chromatography of inorganic cations.

This paper reports on a new suppressor that can be used in the ion chromatography (IC) of inorganic cations. The space in which the electrode is set on both sides of the device is separated into three cells using anion- and cation-exchange membranes. Each of the cells is packed with either an anion- or cation-exchange resin. Anions in the eluent and injected sample are removed by electrical regeneration, based on the electrokinetic phenomenon on both the surface of the ion-exchange resins and the membranes. The electrical conductivity of the suppressed eluent reaches a level similar to that of ultrapure water; therefore, a cation detection limit of sub-ppb order is achieved in IC using the device as a suppressor.

Development of an anti-analyte ion remover used for ion chromatography: Part 1. Examination of a device for anion analysis.

Herein, we report on the fabrication of a device for removing cations of an anti-analyte ion contained in a sample and an eluent under an electric field. The space in which the electrode is set on both sides of the device is separated into three cells using anion and cation exchange membranes. Each of the cells is packed with either an anion or cation exchange resin. Cation removal is performed by electrical regeneration, based on the electrokinetic phenomenon on both the surface of the ion exchange resins and the membranes. It was verified that the developed device has a very low dead volume, and sufficient capacity for the continuous removal of cations from the sample and the eluent. In addition, the detection sensitivity of ion chromatography (IC) was improved using this device as a suppressor, and a detection limit of anions on the sub-ppb order was achieved.